Re: [RFC 00/13] virtio-iommu on non-devicetree platforms

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Fri, Nov 22, 2019 at 08:00:46AM -0500, Michael S. Tsirkin wrote:
> > (2) In addition, there are some concerns about having virtio depend on
> >     ACPI or DT. Some hypervisors (Firecracker, QEMU microvm, kvmtool x86
> >     [1])
> 
> power?

In kvmtool it boot with device tree. It also doesn't need virtio-iommu I
think, since it has its own paravirtualized interface.

> > don't currently implement those methods.
> > 
> >     It was suggested to embed the topology description into the device.
> >     It can work, as demonstrated at the end of this RFC, with the
> >     following limitations:
> > 
> >     - The topology description must be read before any endpoint managed
> >       by the IOMMU is probed, and even before the virtio module is
> >       loaded. This RFC uses a PCI quirk to manually parse the virtio
> >       configuration. It assumes that all endpoints managed by the IOMMU
> >       are under this same PCI host.
> > 
> >     - I don't have a solution for the virtio-mmio transport at the
> >       moment, because I haven't had time to modify a host to test it. I
> >       think it could either use a notifier on the platform bus, or
> >       better, a new 'iommu' command-line argument to the virtio-mmio
> >       driver.
> 
> 	A notifier seems easier for users. What are the disadvantages of
> 	that?

For each device we have to check if it's virtio-mmio, then map the MMIO
resource and check the device type. Having a dedicated command-line
argument would be more efficient.

Thanks,
Jean